Electrical signal apparatus



Feb. 21, 1939. 'l O THOMPSON 2,148,328

ELECTRICAL SIGNAL. APPARATUS Filed June 29, 1956 2 Sheets-Sheet 2 In nu A Li D Patented Feb. 21, 1939 UNITED STATES PATENT OFFICE Philco Radio & Television Corporation, Philadelphia, Pa., a corporation of Delaware Application June 29, 1936, Serial No. 88,016 1n claims. (or 1v1- 119) This invention relates to electrical signaling apparatus and more particularly to novel means for varying simultaneously the frequency response of different portions of a signaling system, such as a radio receiver.A More specifically, the invention provides novel means for Varying the coupling between the primary and secondary windings of the intermediate frequency transformers in a high delity superheterodynel radio receiver and for simultaneously and cooperatively actuating a frequency controll device in the audio frequency portion of the receiver, thus greatly improving the selectivity of the receiver and avoiding certain objectionable characteristics, as hereinafter set forth.

One object of the invention, therefore, is to provide an improved selectivity or frequency response control in a signaling system such as a radio receiver, particularly a receiver of the superheterodyne type, so as to increase materially the fidelity of reception of the receiver.

Another object of the invention is to provide a novel mechanical structure by which the desired control may be accomplished in an economical and eiiicient manner.

A further object of the invention is to provide a mechanical structure of this nature embodying units which may be easily manufactured and assembled, thereby facilitating the manufacture of the device and maintaining the cost of production as low as possible. f

Other objects and features of the invention will appear hereinafter as the description -proceeds.

In the accompanying drawings:

Fig. 1 is a diagrammatic illustration of a'superheterodyne radio receiver embodying the invention;

Fig. 2 is a side elevational view of the control apparatus provided by the invention with one of the units shown in section for the purpose of illustration; Y

Fig. 3 is a sectional view of one of the units taken alongI line 3-3 of Fig. 2;

Fig. 4 is a bottom face View of a portion of the device; and' Fig. 5 is a front face view of the lower portion of the apparatus showing clearly the stop mechanism.

vReferring rst to Fig. 1 of the drawings, there is illustrated a conventional .superhete'rodyne radio receiving system comprising the usual antenna l, the radio frequency amplifier 2, the first detector 3, the oscillator 4, the intermediate frequency amplifier -5. the second detector 6, the

audio frequency amplier 1, and the sound reproducer or loud speaker 8. Such a system is now so well known in the art that it requires no detailed description. As is well known, the intermediate frequency amplifier of such a system 5 comprises one or more transformers which serve to couple the successive vacuum tube amplifiers,

-two windings and thereby vary the frequency re sponse of the transformer. While a sin-gle variable transforme'r is-illustrated diagrammatically in Fig. 1, it will be understood that this is merely indicative of the variability of the several intermediate frequency transformers. While the invention is not limited to any particular range of variation of the coupling between the windings of the intermediate frequency transformers, in general, it will be preferable to vary the coupling within a range from about a half to one and a half or twice critical coupling.-

By thus-controlling the selectivity or transmission characteristic of the intermediate frequency amplifier, that portion of the radio receiver may be adjusted, when desired, to attenuate disturbing signals. In other words, when no disturbingsignals are present, the selectivity control may be adjusted to give broad response throughout the entire signal channel, but when disturbing signals are present, the control may be adjusted to decrease the high frequency response of the receiver so as to attenuate the disturbance signals. It is found, however, that the control of the selectivity or frequency response of the intermediate frequency amplifier does not entirely eliminate the disturbing signals, since there is a certain amount of distortion introduced by the second detector which causes disturbing signals to be transmitted through the audio frequency amplifier to the sound reproducing device or loud speaken For example, a certain amount of cross modulation takes place in the second detector which causes the formation of undesired signals that are supplied to the audio frequency amplier. In further accordance with the invention, therefore, there is provided means for controlling the frequency response or transmission characteristic of the audio amplier in order to attenuate these undesired signals. Furthermore, the frequency control provided in the audio frequency amplifier is correlated with the control of the intermediate frequency amplifier so that the two function cooperatively to vary the frequency response of the system. Thus by controlling the frequency response of boththe I. F. and A. F. amplifiers', undesired signals picked up by the receiver and cross modulation products of the secondvdetector may be attenuated, while still permitting the maximum usable fidelity to be obtained.

The frequency control circuit in the audio amplifier may comprise a potentiometer R and a condenser C serially connected together and in shunt with the signal channel, as is shown in Fig.V 1. In this particular instance, the potentiometer and condenser are connected across the output circuit of the amplifier tube V and the input circuit for the tube V1 is connected to the variable arm of the potentiometer. Thus, variable portions of the resistor R may be included in the input circuit of the tube V1. Grid bias for V1 is supplied through the grid-leak resistor and part of the potentiometer resistance, as will be apparent from the figure. The attenuation of higher frequencies is determined by the position of the variable contact on the potentiometer and obtains from the fact that for low frequencies, the impedance of the condenser will be considerably greater than that of the resistance of the potentiometer. The signal transfer to the tube V1 will be the signal developed across the condenser and that portion of the resistance between the condenser and the variable contact. For signals of low frequency, the impedance of the condenser will be so much greater than that of the potentiometer that the amplitude of the signal transferred will be independent of the position of the variable contact. However, for higher frequency, the impedance of the condenser will be less, since its`impedance varies inversely with frequency andwthus at higher frequencies, the impedance of e potentiometer may become an appreciable portion of the total impedance of the unit and at these frequencies, moving the variable arm towards the condenser will decrease the amplitude of the higher frequency signal supplied to the tube V1. Preferably, the circuits shouldbe so adjusted that the impedance of the condenser for the highest frequency which it is desired to transmit in the most selective position should be somewhat less than the total resistance of the potentiometer. The variable transformer or transformers T and the adjustable potentiometer R are simultaneously operable as indicated by the broken-line representation in Fig. 1. This joint operation or control of these devices is obtained in a novel manner by means of the mechanical structure tobe described later.

Referring now to Figs. 2 to 5 illustrating the mechanical structure of the control device, there is provided a base or support 9 havingdepending end portions III and I I which may be considered, respectively, as front and rear end portions. The rear depending portion II carries the resistor R which may take the form of a conventional device ofthis type. This resistor is provided with a relatively short control shaft I2, rotation of which causes adjustment of a rotary arm (not visible) corresponding to the adjustable arm shownin Fig. 1. The front depending portion III of the base serves to rotatably support a control shaft I3 upon the front end of which there may be provided a control knob (not shown). The shaft I3 carries a pin I4 which is adapted to engage stops I5 (see Fig. 5) provided on the portion III, thus limiting the rrotation of the shaft to a desired range. The opposite end of shaft I3 is formed cooperatively with the free end of shaft I2 and is flexibly coupled thereto by means of coupling I6 which preferably takes the form of the flexible coupling described and claimed in the copending application of Gerald J. Barry, Serial No. 80,630, filed May 19, 1936. It will be understood, of course, that any other suitable coupling may be used. It will be seen that the shaft l2 of the resistor R serves to support the rear end of the control shaft I3, thus eliminating the necessity of providing a second bearing or support for that shaft. Furthermore, the nexible coupling I6 compensates for any slight misalignment of parts that may occur in manufacture and it also enables easy assembly of the parts notwithstanding any such misalignment. It will be understood, of course, that rotation of the control shaft I3 causes corresponding rotation of shaft I2 and, consequently, adjustment of the resistor R.

The shaft I3 also serves to vary the coupling of the transformers T in proper relation to the variation of resistor R.. To this end, there are mounted on the base or' support 9 one or more units I1 depending upon the number of variable transformers and stages employed in the intermediate frequency amplifier. In the specific illustration of Fig. 2, two such units are shown, but it will be understood that any desired number may be used. These units I'I are identical one with another and it is only necessary, therefore, to illustrate and describe one of the units in detail. Each unit comprises a shielding housing or casing I8 within which the other parts are disposed, as shown clearly in Figs. 2 and 3. Where more than one unit is employed, the housings or casings I8 may be placed adjacent one another and may be spot welded together. The transformer T comprises a stationary coil unit I9 and a movable coil unit 20. The coil unit I9 may be attached to a padding condenser 2| by means of a central bolt 22 which alsoserves to secure the assembly to the top of the housing I8 as clearly illustrated. To facilitate assembly of the parts as described in further detail hereinafter, there is provided on the padding condenser 2| an extending stud 23 which serves cooperatively with an opening 2E in the top of the casing I8 to properly position the parts within the casing. The padding condenser 2l serves as a convenient support for the coil unit I9 and the particular assembly of these units is advantageous in that it uses available space to the best advantage and provides for very short leads between each coil and its associated condenser.

The stationary coil unit I9 is provided with a longitudinal recess 25, while the movable coil unit 20 is provided with a cooperating projection 26,1which preferably takes the form of an extending shanlr and plunger-like head 21 adapted to slide within the recess 25. Thus, there is provided a guide for the movable coil unit which serves to maintain the two coil units substantially in axial alignment, while permitting axial movement of the coil unit 20 relative to the coil unit I9. lBy this construction, exact axial alignment is not necessary which facilitates the commercial manufacture of the units. The windings or coils 28 and 29, respectively, of the two coil units are so disposed on the coil supports of the units that when the inner ends of the coil supports abut one against the other, the coils are spaced apart :iol

a predetermined distance and a predetermined degree of coupling exists between them. When, however, the movable coil unit 20 is moved to -some position such as that illustrated, a lesser degree of coupling exists between the two coils and by properly adjusting the movable coil unit, any desired degree of coupling between the coils may be obtained within the range for which the device is adapted.

The coil support of the movable coil unit 20 extends through an aperture 30 provided in the base 9 and this coil support is attached toand is carried by a support or carrier 3| having a transverse lug 32 extending therefrom and having also a longitudinal slot 33 (see Fig. 3). The bifurcated lower portion of support 3| which is thus provided has oppositely extending feetor lugs 34 and `35 between which a strip or plate 36 is attached by means of screws 31 and 38. The portion 39 of shaft I3 is of diminished diameter and extends transversely through the slot- 33. Preferably, this portion of the shaft is provided with anges 4|) forming acircumferential groove therebetween in which the edges of the slot 33 are seated. At the rear of the carrier 3| there is provided `a flexible member 4I which may take the form of a cord having one end fastened to the shaft i3 at 42 and having its other end secured by the screw 38. This member 4I is so arranged that rotation of the shaft I3 counterclockwise, .as viewed in Fig. 3, causes the member 4| to wind up on-the portion 39 ofthe shaft, thus drawing the carrier 3| upward to move the coil unit 20 toward the coil unit I9. When the vshaft I3 is rotated in the opposite direction, however, the member 4| merely unwinds fromy the shaft portion 39 and allows Ythe coil unit 20 to be drawn downward away from the coil unit I9 by the flexible member 43 which4 has one end attached to shaft I3 at 44Cand its other end secured by screw 31. This flexible member passes over the lug 32 and is seated in `retaining recesses thereof,

device is operated.

and it (member `43) is so arranged that rotation of shaft I3 in a clockwise direction, as viewed in Fig. 3, causes the member 43 to wind upon the shaft portion 39, thus exerting a pull upon the lug 32, as will be obvious from Figs. 2 and 3. In this manner, the movable coil unit 20 is moved downward away from the coil unit I9. During the movement of the carrier 3|, the slot ,33, together with the anges 40, maintain the carrier in proper position and prevent lateral movement thereof. l

Within the casing I8, there is provided an apertured insulating plate 45 which carries terminals 46 that project outside the casing on opposite sides of the base 9, as clearly shown in Fig. 3. Electrical connections designated generally by reference character 41 are connected between the terminals 48 and the electrical elements within the casing. Electrical connection to the movable coil 29 from the terminals of the padding condenser 2| are made by means of ne Wires 48 having coiled or helical portions 49 to permit the wires to expand and contract as the coil unit 20 is moved. The wires 49 should besuiciently self-supporting to maintain their positions as the It will be seen from the illustration and the above description that the control shaft I3 serves to actuate the variable resistor R and each of the variable transformers simultaneously and, as above stated, the device is so designed that these elementsare actuated in predetermined relation to one another. The mechanical structure which enables the desired control comprises simple parts which may be manufactured easily and economically and the structure is such that the parts may be easily assembled. Assuming that the parts of the device are in disassembled condition, the assembly of the device may be easily performed as follows.

The upper coil unit I9 is vfirst attached to the padding condenser 2| by means of the bolt 22. The lower coil unit 2D with its carrier 3| attached thereto is then inserted in cooperative relation with the coil unit I9 as illustrated and the wires 48 are connected between the terminals of the padding condenser 2| and the movable coil. The insulating plate 45 is then placed over the movable coil unit and the electrical connections 41 are made between the elements. Each of the transformer units when thus assembled is inserted in its shielding casing I8, the shank 23 being inserted through the opening 24 in the top of the casing. Initially the shank 23 is longer than shown so that it may be grasped at the outside of the casing to draw the assembly into place. The assembly is then secured in place by means of bolt 22 and the shank 23 is cut off substantially ilush with the top surface of the casing, as shown. The shielding casing is then mounted upon the base or support 9.

- s With the resistor R also mounted upon the support 9, the control mechanism is assembled, the control shaft I3 being inserted through the end portion |0 and cooperatively associated with each of the carriers 3| and the rear end of the shaft being exibly coupled to the control shaft I2 of theresistor. With the cords 4l and 43 attached to the shaft I3, the shaft is rotated counterclockwise as viewed in Fig. 3 until the pin I4 abuts against the left hand stop I5, as viewed in Fig. 5. The movable coil unit 20 is moved toward the coil unit I9 and is held thereagainst, while the cord 43 passing about the lug 32 is pulled tightly and is secured by screw 31. 'I'he pulling of thisv cord maintains the shaft I3 in position with the pin I4 engaging the left hand stop I5 and also tends to hold the coil units together. The cord 4I which is looped aboutv the shaft portion I3 is then secured taut by means of screw 38. With the device thus assembled, rotation of the shaft I3 in a counterclockwise direction causes the cord 4| to draw the carrier 3| upward until the coil unit 20 abuts against the coil unit I9, and the coil displacement and control shaft position will be properly orientated with respect to each other.

In one practical embodiment of the invention, the primary and secondary windings of the I. F. transformers each comprised 190 turns of #'1-41 Y Litzendraht wire wound on a one-half inch coil form using a Winding of the universal type. The width of the coils in each case was .18 of an inch and in the position of minimum spacing, which corresponds to maximum coupling, the coils were at `the point at which signal attenuation of 6 decibels occurred, amounted to 51/2 kilo-cycles in the minimum position and 141/2 kilo-cycles in the maximum position. The I. F. unit was thus adapted to transmit a signal of 2% kilo-cycles and '71A kilocycles, respectively. The corresponding cut-off frequency for the audio system in the minimum position amounted to approximately 3 kilo-cycles.

Although the invention has been illustrated and described with reference to a specific preferred embodiment, it will be understood, of course, that various modifications are possible without departing from the scope of the invention. For example, the details of the mechanical structure may be modified while still retaining the principal features of the invention. Other modifications or` changes will occur to persons skilled in the art.

I claim:

l. A device for varying the frequency response of a portion of a radio receiver or the like, comprising at least one variable transformer including a pair of adjacent axially aligned coil units, one of said units comprising a hollow cylindrical coil form and the other unit comprising a coil form axially adjacent said hollow form, an-

axially projecting shank or stem on said second coil form of smaller diameter than the internal diameter of said hollow form and extending freely into the latter, a cylindrical head on the end of said stem slidably seated in said hollow form, wherebyaxial movement and some radial movement of one unit relative to the other is permitted, a rotatable shaft, and means operable by said shaft for moving saidmovable unit relative to the other unit to vary the coupling between the coils thereof.

2. A device for varying the frequency response of a portion of a radio receiver or the like, comprising at least one variable transformer including a pair of adjacent axially aligned coil units each comprising a cylindrical coil form, one of said units being movable axially relative to the other unit, a carrier for said movable unit extending axially from an end of the coil form of the movable unit and having a guide portion, a rotatable shaft extending transversely of said carrier and having a portion seated in said guide portion, and means operable by said shaft for moving said carrier to thereby move said movable unit relative to .the other unit to vary the coupling between the coils thereof.

3. A device for varying the frequency response of a portion of a radio receiver or the like, comprising at least one variable transformer including a pair of adjacent axially aligned coil units each comprising a cylindrical coil form, one of said units being movable axially relative to the other unit, a carrier for said movable unit extending axially from an end of the coil `form ofthe movable unit and having a guide slot therein, a rotatable shaft extending transversely of said carrier and having a portion seated in said slot, and flexible connections between said carrier and said shaft adapted to move ysaid carrier when said shaft is rotated, to thereby move said movable unit relative to the other unit to vary the coupling between the coils thereof.

4. A device for varying the frequency response of a portion of a radio receiver or the like, comprising at least one variable transformer including a pair of adjacent axially aligned coil units, one of said units being movable axially relative to the other unit, a carrier for said movable unit having a lug thereon and a guide slot therein, a rotatable shaft having a portion seated in said slot, a exible connection between said carrier and said shaft for moving said carrier in one direction, and another flexible connection engaging said lug and fastened between said carrier and said shaft for moving said carrier in the opposite direction, whereby said movable unit may be moved relative to the other unit.

5. A device for varying the frequency response of a portion of a radio receiver or the like, comprising at least one variable transformer including av pair of adjacent axially aligned coil units, one of said units being movable axially relative to the other unit, a carrier for said movable unit 6. A device for varying the frequency response of a portion of a radio receiver or the like, cornprising at least one variable transformer including a pair of adjacent axially aligned coil units, one' of said units being movable axially relative to the other unit, a carrier for said movable unit having a lug thereon and transverse extensions spaced from said lug, a rotatable shaft arranged cooperatively with said carrier, a flexible connection between one of said extensions and said shaft for moving said carrier in one direction, and another flexible connection engaging said lug and fastened between another of said extensions and said shaft for moving, said carrier in the opposite direction, whereby said movable unit may be moved relative to the other unit.

'7. A device for varying the frequency response of a portion of a radio receiver or the like, comprising at least one variable transformer including a pair of adjacent axially aligned coil units, one of said units being movable axially relative to the other unit, a slotted carrier for said movable unit having a lug thereon and transverse extensions spaced from said lug, a rotatable shaft having a portion seated in said slot between said lug and said extensions, a flexible connection between one of said extensions and said shaft for moving said-carrier in one direction, and another flexible connection engaging said lug and fastened between another of said extensions and said shaft for moving said carrier in the opposite direction, whereby said movable unit may be moved relative to the other unit.

8. A device for varying the frequency response of a portion of a radio receiveror the like, comprising at least one variable transformer including a pair of adjacent axially alignedcoil units, one of said units being movable axially relative to the other unit, a carrier for said movable unit having a guide slot therein, a rotatable shaft having a portion seated in said slot, a flexible connection between said shaft and a part of the carrier adjacent one end of said slot for moving said A carrier in one direction, an element on said carrier adjacent the other end of s aid slot, and another flexible connection engaging said element and fastened between said shaft and the said part of the carrier for moving said carrier in the opposite direction, to thereby vary thel coupling between the coils of said units.

9. A device for varying the frequency response of a portion of a radio receiver or the like, comprising at least one variable transformer including a pair-of axially aligned coil units, one of said shaft arranged cooperatively with said carrier, a

flexible member extending between said carrier and said shaft and arranged toiwind about the shaft when the shaft is rotated in one direction -so as to`move the carrier in one direction, and another flexible member extending between said carrier and said shaft and arranged to wind about the shaft when the shaft is rotated in the opposite direction so as to move the carrier in the opposite direction.

10. A device for varying the frequency response of a portion of a radio reeiver or the like, comm prising at least one variable transformer including a pair oi' axially aligned coil units, one of said lunits being movable axially relative to the other unit, avcarrier for said movable unit, a rotatable shaft arranged cooperatively with said carrier, a flexible member operatively engaging a portion of said carrier on one side of said shaft and connected to the shaft so as to Wind thereabout when the shaft is rotated in one direction and thus move the carrier in one direction, and another flexible member operatively engaging a portion of the carrier on the other side of said shaft and connected to the shaft so as to wind thereabout when the shaft is rotated in the opposite direction so as to move the carrier in the opposite direction.

ELMER O. THOMPSON. 

